This invention relates to a novel floating wave attenuator. More particularly, this invention pertains to a novel design of floating wave attenuator which has a curved vertical wave attenuating wall section, a bottom vertical motion braking flange, and an air chamber for adjusting buoyancy.
Floating breakwaters have been used for many years. Historically, a professional paper entitled xe2x80x9cOn Floating Breakwatersxe2x80x9d was authored by Joly as far back as 1905. Perhaps the first major application of floating breakwaters was by the British during the Second World War. The Bombardon and Phoenix floating breakwaters were designed for use in the Normandy invasion of 1944. Notably, both were destroyed in a major storm.
In 1971, the United States Navy made a survey of floating breakwater concepts. The Navy found 106 different concepts that were either under current study, had been studied in the past, were in use, or had been used in the past.
Later, in 1981, the U.S. Army Corps of Engineers made a literature study of the then state-of-the-art in floating breakwaters. Although previous studies recognized at least sixty different groupings of floating breakwater concepts, the Corps study reduced the groupings further through geometric and functional similarities to ten major types of floating breakwaters. These major groups are:
(1) pontoon
(2) sloping-float (inclined pontoon)
(3) scrap-tire
(4) A-frame
(5) tethered-float
(6) porous-wall
(7) pneumatic and hydraulic
(8) flexible-membrane
(9) turbulence-generator
(10) peak energy dispersion
Although these studies and reports appear to reference a large number of floating breakwater concepts and describe a number of prototype installations, the fact is that very few floating breakwater concepts have actually matured into a commercially available product.
Normally, one of two general physical principles can be used to explain the wave attenuating ability of a specific floating breakwater. The first is turbulence and the second is reflection.
The general characteristics of turbulence-type breakwaters are low draft, generally large width with respect to the wave size most effectively attenuated, and flexibility. The most obvious physical measurement of turbulence-generating breakwaters that directly relates to the effectiveness of this type of breakwater is its width. The width of a turbulence-type breakwater should generally be at least equal to 1.0 to 1.5 times the wave length of the design wave. More is better. It is normally not necessary for a turbulence-generating breakwater to be rigid, and in fact, most breakwaters are characterized by the flexibility of the entire breakwater system.
Perhaps the best well known turbulence-generating breakwater is the floating scrap-tire breakwater. It is made by connecting tires together and floating them with cubes of styrofoam. The floating scrap-tire breakwater attenuates waves through a loss of energy caused by the multiple openings and xe2x80x9ctrapsxe2x80x9d through which the water must pass to get to the lee side. Basically, the maze of channels exhausts the force of the wave on its way through the springs.
Another form of wave turbulence attenuation is caused by friction during the movement of water along the bottom of a large flat plate. This is how a large flat raft can be used to stop waves. The plate, or raft, must be somewhat rigid when used in this way, and must be very wide with respect to the design wave.
The second general mechanism used to stop waves is reflection. The best reflectors are probably bulkheads. When a wave hits a flat shoreline bulkhead, it is almost entirely reflected. A floating breakwater that uses reflection to stop waves must have characteristics similar to a shoreline bulkhead if it is to be as efficient. Reflective-type floating breakwaters do not need as much width as a turbulence-inducing-type floating breakwater. The key to the highly effective reflection characteristics of a shoreline bulkhead is the mass of earth behind the bulkhead which prevents the bulkhead from moving. Similarly, rigidity in the water is the key characteristic required of a floating breakwater that relies on reflection to stop waves. If the entire breakwater, or some component of the breakwater, is able to move significantly in the water, the wave attenuation capabilities of that reflective surface are greatly reduced.
A second characteristic required for effective operation of a reflective-type breakwater is depth penetration or draft. Without sufficient draft, much of the wave energy will pass below the breakwater and will rebuild waves on the lee of the breakwater. Thus, the two key criteria for effective operation of reflective-type breakwaters are rigidity, or lack of movement in the water, and depth penetration, or draft.
E. Douglas Sethness, Jr., President, Waveguard International, Austin, Tex., in an article entitled xe2x80x9cA Survey of Commercially Available Floating Breakwatersxe2x80x9d, described the floating breakwater products, known to the author, that are commercially available on a continuing basis in the United States and Canada. According to him, these commercially available floating breakwaters can be divided between the following two general categories:
Reflective-type United McGill Cylindrical Float
WAVEGUARD
Meeco Hanging Panel
Unifloat Caisson
Turbulence-Generation Wallbreak
Scrap-tire
American Docks Raft-type
The purpose of the Sethness article was to inform the marina or small boat harbor owner of the more important aspects of evaluating the use of a floating breakwater at a given site. The decision process that is presented in the article was intended to aid the owner or developer in understanding the location, engineering, expected performance, and risk/benefit analyses that should be an integral part of that evaluation.
According to Sethness, there is no substitute for properly understanding the breakwater site conditions. This first and most basic step is the one most generally glossed over in the process leading to the purchase of a floating breakwater system. A proper wind and wave analysis is crucial. Then, although there are generally understood requirements for marina construction, a set of specifications that defines the performance criteria for floating structures inside the marina must be developed. Understanding the structural and operational capabilities of the boats and marina facilities is extremely beneficial when defining the necessary performance characteristics of the breakwater. The third point that should be fully understood by a breakwater purchaser is the risk involved. A floating breakwater will not stop all of the waves, particularly freak waves. The proposed breakwater system should havesome understandable means of scaling itself to the design wave. One size breakwater does not fit all conditions.
In conclusion, the Sethness article states that floating breakwaters are a practical means of solving some of the problems faced by marina and small boat harbor owners when they are required to expand into less well protected waters. Floating breakwaters may be the only alternative available for wave protection in areas that are environmentally sensitive, where there are boundary or navigation constraints, or where the water is very deep. However, as with many other things, a floating breakwater will perform only as well as the input, in terms of investigationtime and engineering, that has preceded its installation.
A number of patents disclose various designs of floating breakwaters. These include the following:
The invention is directed to a floating wave attenuator comprising: (a) a curved vertical wall having an exterior surface and an interior surface;(b) a flange associated with the wall and extending from at least one of the exterior surface and interior surface of the wall; and (c) an air chamber in the wall, the air pressure in the chamber being adjustable to govern the buoyancy of the wave attenuator. In alternative embodiments, the vertical wall can be straight or segmented.
The base flange of the attenuator can extend from the bottoms of both the exterior and interior surfaces of the curved vertical wall. The curved vertical wall can be hollow and at least part of the interior of the wall can be filled with a flotation material. The flotation material can be expanded polystyrene foam. The wave attenuator can include an air chamber below the flotation material in the interior of the curved wall. In alternative embodiments, the bottom face of the base may have irregular indentations to increase friction.
The intersections between the bases of the exterior and interior surfaces of the curved vertical wall and the base flange can be reinforced. The reinforcing members can be triangular shaped trusses which can be disposed at periodic locations along the length of the exterior and interior surfaces of the curved wall and base flange. The top surface of the curved vertical wall can be flat and can include a railing along its length.
The wave attenuator can be deployed on a body of water and can be anchored. The anchors can be secured to one or more of the triangular shaped trusses.
The expanded polystyrene foam can be of different density at different elevations in the interior of the vertical wall. The air chamber in the interior of the vertical wall can have one or more openings therein to enable water to circulate from outside into the air chamber.
Two or more wave attenuators according to the invention can be linked together in a serial pattern to form a breakwater which can be deployed on a body of water. The series of wave attenuators can be linked together in a consistent curved pattern so that the interior surfaces of the plurality of wave attenuators are all on one side and the exterior surfaces of the plurality of wave attenuators are on an opposite common side. The series of wave attenuators can be linked together so that the exterior and interior surfaces of each the wave attenuators in the series alternate in serial pattern along the length of the linked wave attenuators.